The present invention relates to a method and apparatus for detecting discontinuities, such as bubbles, in a fluid flow utilizing ultrasonic energy.
Various arrangements have been proposed for detecting bubbles in a flow of liquid, particularly where the liquid is in a tubing which is either rigid or compressible. Some of the uses for such a bubble detector would be, for example, in detecting air bubbles in body fluids, such as blood, which are being transmitted from one place to another either with the patient in the transmittal loop or from one type of a machine, such as blood processing machine, to another such machine.
Some known bubble detectors, particularly those detecting on the basis of amplitude of received signal, have a problem in detecting the bubbles caused by the size of the tube in which the fluid flows, the aging of the tube, which reduces its wall thickness and its flexibility, tube wall thickness and also with respect to bubble size. All of these problems give rise to variations in amplitude of the detected received signal. For a constant gain and constant threshold circuit, reliable detection of an air bubble becomes a serious problem.
Dam U.S. Pat. No. 4,607,520, owned by the assignee of the present application, discloses a method and apparatus for detecting bubbles in a stream of liquid flowing in a tube by the use of pulsed ultrasonic energy. Bursts of pulses of ultrasonic energy are transmitted from a transmitting transducer to a receiving transducer. A tube in which the fluid, perhaps containing bubbles, flows is held between the two transducers. The time of arrival of the signals is measured and signal processing is performed to ensure reliable detection. If there are bubbles in the line, then no signals are detected and this state is also detected.
The above described bubble detectors typically operate off a five volt supply and require about 25 milliamps of current. These requirements necessitate use of an appropriate power supply, and effectively preclude its use in battery powered systems.
The present invention is directed to an improvement in the above described bubble detectors.
In accordance with the invention there is provided a low voltage, low current detection circuit in a novel bubble detector.
A further object is to provide a method and apparatus for detecting bubbles in which pulsed ultrasonic energy is used. Still another object is to provide a bubble detector in which bursts of ultrasonic energy are used and the received bursts are signal processed.
There is disclosed herein an apparatus for detecting a discontinuity in a stream of fluid flowing in a tube. The apparatus includes a sensing means having spaced apart transmitting and receiving transducers, the tube disposed in a space between the transducers. Supply means are provided for connection to a relatively low voltage power source. A discontinuity detection circuit is operatively coupled to the supply means and the sensor. Transmit means supply successive bursts of pulse of electrical energy to the transmitting transducer to cause it to vibrate to produce corresponding bursts of pulses of sonic energy which are transmitted through the tube to the receiving transducer. There is a predetermined time of no pulse production between successive bursts of pulse. The receiving transducer converts the bursts of pulse of received sonic energy into corresponding electrical signals during the predetermined time between the successive bursts. An amplifier circuit is connected to the receiver transducer for amplifying the received electrical signals. The amplifier circuit comprises a transistor amplifier circuit drawing less than about ten milliamps from the supply means. Receive means are responsive to the amplified electrical signals during the predetermined time for producing a first signal corresponding to the pulses of the transmitted pulses of a burst in response to the presence of the fluid and a second signal in response to the presence of a discontinuity in the fluid. Means are responsive to receipt of the first or second signals to produce an output corresponding to the presence of the fluid or a discontinuity in the fluid.